Hysteresis motor control system and method of operation



Jan. 4, 1949.

H. C. ROTERS HYSTERESIS MOTdR CONTROL SYSTEM AND METHOD OF OPERATION Filed Aug. 9, 1946 I 2 Sheets-Sheet l Hysteresis Rotor 15. I4 IMiA HVVENTUR. HERBERT C. ROTERS H. C. ROTERS Jan. 4, 1949.

HYSTERESIS MOTOR CONTROL SYSTEM AND METHOD OF OPERATION 2 Sheets-Sheet 2 Filed Aug. 9, 1946 FIG.7d-.

INVENTOR. HE'FMERT C. ROTERS FIG.6.

Patented Jan. 4, 1949 HYSTERESIS MOTOR CONTROL SYSTEM AND METHOD OF OPERATION Herbert 0. Roters, Kew Gardens, N. Y., assignor, by mesne assignments, to Casner Patents, Inc., New York, N. Y., a corporation of New York Application August 9, 1946, Serial No. 689,386

22 Claims.

This invention relates to hysteresis motor control systems and methods of operation thereof and more particularly to such systems and methods effective to reduce the magnetizing current of the motor under normal operating conditions.

In applicants prior patent, No. 2,328,743, there is described and claimed a method of operating a hysteresis synchronous motor at an abnormally high magetomotive force either during the period of acceleration to synchronism or momentarily at synchronism, for the purpose of reducing the magnetizing current. of the motor during normal operation. This invention is directed to a system for effecting this over-magnetization" automatically without the necessity of manual switching or personal supervision. In order that the full benefits of over-magnetization be realized, it is-necessary that the over-magnetization be applied to the motor momentarily while it is in synchronism or at least up to the point at which synchronism is reached. Therefore, any automatic switching means utilized to effect this overmagnetization must be accurately sensitive to the condition of synochronism and maintain such over-magnetization until synchronism is reached. Ordinary devices which have been commonly used in the prior art, such as centrifugal switches, forthe purpose of controlling the starting of motors are not sufficiently accurate and are, therefore, not suitable for this purpose.

It is an object of the invention, therefore, to provide a new and improved hysteresis motor control system for effecting momentary overmagnetization of the motor at or during synchronism to reduce the normal magnetizing current of the motor.

It is another object of the invention to provide a new and improved method of operation of hysteresis motors in which the over-magnetization of the motor is effected automatically in response to the acceleration of the motor.

In accordance with the invention, an electrical control system for a hysteresis synchronous motor including a magnetic armature of material having a high hysteretic constant comprises an acceleration-responsive device adapted to be driven by the motor. circuit-controlling means disposed to be actuated by the device, and an energizing circuit for the motorv including the circuit-controlling means for developing in the motor an abnormally high magnetomotive force.

Further in accordance with the invention, a method of operating a hysteresis synchronous motor including a magnetic armature of material having a high hysteretic constant comprises operating the motor at an abnormally high magnetomotive force whenever the acceleration of the motor is above a given value and reducing the magnetomotive force of the motor whenever the acceleration of the motor is less than such value, thereby to reduce the normal magnetizing current required by the motor.

Further in accordance with the invention, a method of operating a hysteresis synchronous motor including a plurality of phase windings and a magnetic armature of a material having a high hysteretic constant comprises, operating one phase winding of the motor momentarily at an abnormally high magnetomotive force to magnetize the armature. and thereafter reducing the magnetomotive force of such phase winding to its normal value, thereby to reduce the normal magnetizing current required by the motor.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring now to the drawings,

Fig. 1 represents a hysteresis motor control system, partially schematic, embodying the system of the invention and capable of operating in accordance with the method of the invention; Fig. 2 is an end view of an alternative form of acceleration-responsive device suitable for use in the system of Fig. 1; Figs. 3-6, inclusive, are circuit diagrams of alternative lectrical systems for effecting over-magnetization of a hysteresis motor and suitable for actuation by the acceleration-responsive device of Fig. 1 or Fig. 2; while, Figs. la-7d, inclusive, are simplified winding connections of the motor of Fig. 6 effected in the several positions of the acceleration-responsive device.

Referring now to Fig. 1 of the drawings, there is represented an electrical control system for a hysteresis synchronous motor ID. The motor It includes one phase winding Illa connected across alternating-current supply terminals ll through a phase-shifting condenser l2 and a second multi-section phase winding lllb provided with intermediate winding terminals 10c, lid and an end terminal lfle. The motor is also provided with a magnetic armature member If of material having a high hysteretic constant, for example, an aluminum-nickel-cobalt alloy, commercially available under the trade name Alnice."

The control system of Fig. 1 also includes an acceleration-responsive device it adapted to be driven by the motor It in'any conventional manner, as by mounting it directly on the motor shaft, gearing it thereto or, as illustrated, by means oi a flange coupling ll. The device It includes a driven member, such as a shaft in, having a threaded portion lib and connected to be driven by the motor shaft through the coupling H. The device ll also includes an inertia member having a lost-motion driving connection with the driven shaft I311, this driving connection having a resilient link. Specifically, the inertia member may be a flywheel lic threaded on and axially movable along the portion lib of the shaft I31: and the resilient link may be a helical torsion spring lid, connected at one end to the shaft Ila. and at the other end to the flywheel lic, as illustrated, and effective to drive the flywheel lic from the shaft Ila.

The system of Fig. 1 also includes circuit-controlling means disposed to be actuated by the acceleration-responsive device II, this circuit-controlling means being in the form of a leaf-spring switch I! comprising a leaf spring lBa rigidly mounted at one end on a support lib and resting at the other end against a flxed support He. The member I50 is disposed to be displaced from the rest le by axial movement of the inertia flywheel l3c along the threaded shaft portion llb whenever the acceleration of the motor In is above a given value, for example, substantially above zero. To this end, there is attached to the flywheel I30 a cup-shaped member ile disposed to engage the spring member I56 upon relatively small initial axial movement of the flywheel l3c along the shaft portion I3 I). The switch It may be provided with normally open or normally closed contacts, or both, in accordance with the controlling functions desired. For example, the switch l5 illustrated is provided with a pair of normally closed back contacts IM and a movable contact 152 forming with stationary contacts and IE9 normally open contacts l5e, l5f and lie, lily.

The control system of Fig. 1 also includes an energizing circuit for the motor including the circuit-controlling means or switch it for developing in the motor an abnormally high magnetomotive force. The circuit-controlling means may be connected in a variety of ways to control the energization of the motor windings. In the system of Fig. 1, the switch it is connected to modify the connections of the sections of the phase winding lllb; specifically to decrease the number of winding sections energized when the motor acceleration is substantially above zero. For example, the switch l5 has a first position, in which it is illustrated, corresponding to substantially zero acceleration of the motor in which its normally closed contacts l5d are effective to connect one side of the supply circuit to the intermediate terminal llld to include an intermediate number of sections of the phase winding lllb in the energizing circuit; the switch l5 also has a second position, corresponding to initial movement of the inertia member I30 along the threaded shaft portion I3b, in which the contacts l5d are open while the contacts l5e, l5f are closed to connect the supply circuit terminals to the outer winding terminal llle of phase winding lllb, thus to connect the maximum number of winding sections in series across the supply circuit to develop a subnormal starting magnetomotive force; while the switch l5 has a third position in which the contacts l5e, Illg are closed, which occurs an appreciable interval later corresponding to the movement of the flywheel I30 to its extreme righthand position, in which the supply circuit terminals are connected to the lowest terminal lie of the phase winding lib so that only a single winding section is connected across the supply circuit, resulting in the development of an abnormally high magnetomotive force in the motor.

It is believed that the operation of the motor control system of Fig. 1 will be apparent to those skilled in the art from the foregoing description. In brief, the method of operation of the system is as follows: In the positions of the several elements of the system as shown in Fig. 1, with the contacts id of the switch l5 closed, the supply potential across the terminals H is applied to the intermediate terminal llld of the phase winding Iflb and this phase winding, in conjunction with the phase winding Illa excited through the phase-shifting condenser l2, produces a rotating magnetic field causing the hystercsis motor ill to rotate in a manner well understood in the art and as described more fully in applicants prior Patent No. 2,328,743, granted September 'I, 1943, and entitled Self-starting hysteresis motor." However, as soon as the motor ill commences to rotate, the resilient driving spring l3d interconnecting the shaft lid and the flywheel I3c permits the latter to lag behind the motor rotation due to its inertia, so that it moves axially to the right along the threaded shait portion I317. The initial movement of the flywheel i3c actuates the spring member lid to open the contacts l5d quickly, so that an intermediate value of magnetomotive force resulting from applying the supply voltage to the intermediate tap illd is developed only momentarily and may, as a practical matter, be disregarded. Immediately thereafter, continued movement of the flywheel l3c actuates member lid to close the contacts lie, 15! to complete the connections from thesupply circuit to the outer terminal llle of the phase winding illb. This connection of the supply circuit across the full winding I022 results in the development in the motor ill of a minimum or subnormal magnetomotive force for starting the motor. The eflect of this is to limit the magnitude of the motor starting current and to limit the initial torque developed by the motor which might tend to injure any connected load. It is well understood that, in the case of motors of appreciable size, it is frequently dcsirable to limit the starting current to a moderate value for a variety of reasons. However, when subnormal starting current is not required, it will be understood that the contact l5f may be omitted and the contacts l5e and l5g arranged to close substantially immediately after the opening of contacts lid.

As the motor l0 accelerates toward synchronous speed, the flywheel I30 lags farther behind the rotating shaft lid and continues to move axially to the right, as shown in Fig. 1, until, in its extreme position, the contacts l5e, l5 are open and, immediately thereafter, the contacts lie and lip are closed, completing the circuit from the supply terminals II to the terminal lllc of the winding lOb, thus connecting only a single section of the phase winding lOb directly across the supply circuit and developing in the motor l 0 an abnormally high magnetomotive force. This last connection is made whenever the acceleration oi the motor Ill is above a given value, preferably any value substantially above zero, for a sufficient interval to provide movement of the flywheel l3c along the threaded shaft Ilb to its extreme right-hand position.

when the motor reaches synchronous speed,

'aiaa'ioo its acceleration drops to zero and may, in certain cases, become negative in case the motor overshoots synchronism lightly. When the acceleration falls below that effective to cause the flywheel lie to lag behind the shaft [3a against the torsion of the spring l3d, and preferably when it has dropped substantially to zero, the spring lid returns the flywheel l3c to the position illustrated in Fig. 1 and the contacts of the switch ii are operated in a reverse sequence until the contacts lid are again closed, corresponding to normal operation of the motor, at which the supply circuit terminals II are connected to the intermediate terminal "id of phase winding lllb, thereby reducing the magnetomotive force developed in the motor ill to its normal value.

- As explained in more detail in the aforementioned Patent 2,328,743, this momentary overmagnetization of the motor In at or near synchronous speed over-excites the rotor l0! so that the motor l0 operates effectively as a normally excited or over-excited synchronous motor, rather than as an under-excited synchronous motor,

The device It comprises a hub I a mounted on shaft Ila and having a radial arm lib from which are supported resilient contact arms Ito and lid carrying relatively movable contacts lie and IBI. respectively. The contact arm Ito also carries at its outer end an inertia mass or weight Hg. The device is also provided with an angularly displaced radial arm llh on the outer end of which is carried a dashpot Ni and plunger I81 connected by an arcuate link ltk to the contact arm lBc.

In the arrangement of Fig. 2, acceleration of the shaft Ila in the direction indicated by the arrow is effective to cause the mass ligto lag behind the other movable portions of the device, resulting in the closing of the contacts lee, It] so long as the acceleration oi the motor is above a predetermined minimum value, preferably substantially above zero. Obviously, whenever the acceleration of the shaft Ila drops below such value, the resilient contact arm I80 will restore the mass I 80 toits normal position, illustrated in Fig. 2, opening the contacts lie, IS The effect which is the normal method of operation of a hysteresis motor. The result of thisover-excitation of the rotor III! is to cause the motor to draw reduced magnetizing current, reduced resultant current, with a corresponding reduction in copper losses, and to operate at or near unity power factor, all of which operating characteristics are of well-recognized desirability. This over-magnetization of the motor during starting also increases the starting torque during the portion of the starting cycle in which it is efiective and also increases the synchronizing torque or the motor.

It is to be noted that in the system of Fig. 1 only the phase winding Iflb is momentarily over-excited in response to acceleration of the motor I'O, for the purposes described, as this considerably simplifies the switching mechanism. However, it has been shown by experiment that the over-magnetization of a single-phase winding of such a polyphase hysteresis motor procures substantially the same beneficial reduction in normal magnetizing current and improvement in power factor as does a momentary over-magnetization of all phase windings. It is to be understood, therefore, that when reference is made to developing an abnormally high magnetomotive force in the motor, it is intended to refer to the over-excitation of one or all of the motor phase windings.

It is to be further noted that, upon the closing of the contacts I5e, l5g resulting in over-magnetization of the motor iii, the torque developed by the motor and its acceleration are further increased, with the result that the inertia flywheel i3c is stillmore strongly urged to its right-hand position and increases the contact pressure between the contacts I See, i5g, thereby avoiding any fluttering of the contacts which would result in erratic behavoir of the motor. It is to be further noted that. the electrical system of Fig. 1 includes no slip rings or commutator but that the modification of the circuit connections is effected solely by the opening and closing of fixed contacts and co-operating movable contacts carried by the switch member l5a.

In Fig. 2 there is represented an alternative form of acceleration-responsive device It in which, for the sake of simplification, there are illustrated only a single pair of normally open contacts, although it will be understood that the number and type of contacts may be selected in accordance with the functions to.be performed.

of the dashpot I61 and plunger I81 is to control the rate of movement of the mass llig between the circuit opening and circuit closing positions,

thus introducing a time delay into either or both of these operations. It is further efl'ective to stabilize the mass I8 and to prevent a fluttering of the contacts lie, it, near the point of transition between circuit opening and circuit closing positions. I

In Fig. 3 there is represented a modification of the control system of the invention as applied to the operation of a. two-phase motor 20 from twophase alternating-current supply circuit terminals 2|. The motor 20 comprises an armature 20] which may be like the armature ID) of the motor i0, and is provided with main phase windings 20a and 2% connected directly to the supply circuit terminals 2| and with auxiliary starting windings 20c and 20d associated with the Windings 20a, 20b, respectively, and adapted to be connected in parallel therewith through a twopole switch comprising contacts 22a, 22b actuated by a mechanism indicated schematically at 220, which may be the acceleration-responsive device of either Fig. 1 or 2. If desired, only one auxiliary starting phase winding need be supplied, in which case only one of the contacts 22a, 22b need be provided.

The operation of the system of Fig. 3 is in all respects similar to that of Fig. 1 described above; the motor windings are somewhat more complicated and, therefore, somewhat more expensive, but it has the advantage of a completely symmetrically rotating field during starting and synchronizing, which imparts to the motor a somewhat higher synchronizing torque.

In Fig. 4 there is represented a further modifled form of the control system of the invention including a two-phase motor 30 having an armature 30] which may be similar to the armature ID of the motor In. The motor 30 is provided with two phase windings, each made up of two sections; namely, the sections 30a and 30b making up one phase winding, and the sections 390 and 30d making up the other phase winding.

The system also includes circuit-controlling means, specifically the switch contacts 33 and 34, effective to change the number of winding sections energized. Specifically, the switch contacts 33 and 34 are adapted to be operated by an acceleration-responsive device indicated schematically at 35. The switch contact 33 is movable between the contacts 33a and 33b simultaneously with movement of the switch contact 34 between contacts 34a and 3412. With the switch contacts 33 and 34 in the positions illustrated in Fig. 4, the motor phase windings are excited normally by direct connection in series across the supply circuit terminals 2|, 2|. When the switch contacts 33 and 34 are moved to engage contacts 33b, 34b, respectively, in response to acceleration of the motor above a given value, only the winding sections 3022 and 300 are connected across the supply terminals 2|, thus developing an abnormally high magnetomotive force in both phase windings and-over-exciting the motor in accordance with the principles outlined above. During the movement of the switch contacts between these positions, the resistors 3i and 32 serve to provide circuit continuity. If the switch arms were allowed to bridge the contacts during the transition, sections 30a and lllc of the motor winding would be momentarily short-circuited, causing severe arcing at the contacts. Resistors 3| and 32 are preferably selected of such a value as to maintain a minimum torque during the transition. When the motor is started without load or under light load, these resistors can be omitted, provided that the rotor does not slow down perceptibly below synchronism during this period. If the resistors 3i and 32 are of too low an impedance value,

undesirably large circulating currents will flow while the movable contacts engage contacts 33b and 34b.

In the modification of the invention represented in Fig. 5, the two-phase motor 40 is provided with an armature 40f which may be similar to the armature lllf of the motor Ill. The motor 40 is further provided with single-section or untapped phase windings 40a and 40b, the former being connected directly across the single-phase alternating-current supply terminals II and the latter being normally connected across the terminals ii through a phase-shifting condenser 4|. It is to be noted that the condenser 4| eflectively comprises impedance means normally in circuit with the phase winding 40b of the motor.

The system further includes circuit-controlling means, such as a movable switch contact 42 effective to reduce the value of the impedance means effectively in circuit with the motor. Specifically, there is provided an auxiliary condenser 43 adapted to be connected in parallel with the condenser 4| by means of the switch contact 42. It will be understood that the switch contact 42 is adapted to be operated by the acceleration-responsive device of either Fig. 1 or Fig. 2. Upon its operation, the connection of the condenser 43 in parallel with the condenser 4| reduces the impedance effectively in series with the phase winding 40b, thus increasing the current therein and the magnetomotive force developed thereby. It will be clear that the principles of operation of this modification are similar to the previously described modifications.

In Fig. 6 there is represented an electrical control system for changing the connections of a plurality of winding sections of each oi. the phase windings of a polyphase motor from series to parallel connection in response to the acceleration of the motor to develop the desired abnormally high magnetomotive force. Specifically. in the system of Fig. 6 the hysteresis motor 50 comprises an armature 50! which may be similar to the armature Hi] oi the motor Hi. The motor 50 also includes a first phase winding made up i of winding sections 50a and 50b and a second phase winding made up of winding sections We and Md. The windings 53a, 50b and We, Ild are connected to be excited through a circuitcontrolling mechanism or switch II from the twophase alternating-current supply circuit terminals 2|.

The switch 5| includes four movable contacts 5|a, 5|b, 5|c, and 5|d mounted on spring arms secured to a fixed support He. These movable contacts co-operate with four fixed contacts 5|}, 5| g, 5|h, and iii. The four spring contacts Bic-Sid, inclusive, are adapted to be actuated by a common reciprocable operating arm 5|! adapted to be actuated by an acceleration-responsive device such as that illustrated in Fig. l or Fig. 2. The contact arms of the spring contacts Sid and 5|c pass through relatively narrow apertures in the actuatingarm 5|;i, while the .-pring arms of the contacts Gib and Bid pass through relatively wide apertures in the member 5i7', so that, in a second position of the swltch, a contact is made between contacts 5|a and 5|! and 5|c and 5|h before it is broken between contacts Sit) and 5| and 5|d and 5|h. Subsequently, in a third position of the switch, contacts are broken between contacts 5|b and 5|,f and, in a fourth position, contacts are made between contccts SH) and Sly and between contacts 5|d and 5h. The contacts between contacts Sid and 5|] and between 5|c and Sin are maintained in the second, third, and fourth positions of the switch. The result is effectively a iour-position switch which changes the winding connections oi! each of the phases in accordance with the simplified circuit connections of Figs. 7a-'ld, inclusive. representing the change in connections of the winding sections 50a and 501). Thus, in the first position of the switch 5| illustrated, the windings 50a and 50b are connected in series across one phase of the supply circuit terminals 2|. In the second position of the switch, the winding 50a is short-circulted by the contacts 5|a, III, 5 |b so that only the winding section 50!) remains in circuit. In the third position of the switch 5|, the contacts 5| b, 5| are broken, thus remov-' ing the short-circuit from the winding 50a and leaving it on open-circuit while the winding 50b remains connected across one phase of the supply circuit terminals 2|. In the fourth and final position of the operating member 5h, the windings 50a and 50b are connected in parallel through the contacts 5|b and 5|a and the contacts Sid and 5|]. The spacing of the several stationary and movable contacts of the switch 5| is such that. in the transition from the series connection in the section of Fig. 7a to the parallel section of Fig. 7d, the circuit through one or both of the winding sections of each phase winding is at no time interrupted. This type of circuit control is ideal in minimizing the duty on the circuitcontrolling switch and eliminating the requirement for discharge resistors or condensers which. in some instances. may more than compensate for the additional complexity.

It will be understood that the operation of the system of Figs. 6,-7a-7d, inclusive. is in all respects similar to that described above, normal magnetization being effected in the position 01' the switch hysteresis motor whenever the acceleration of the motor is above a predetermined value, preferably substantially above zero, in orderto reduce the normal magnetizing current of the motor said one phase winding to its normal value,

and thus to improve its eillciency and its power factor.

While there have been described what are at present considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. The method of operating a hysteresis synchronous motor including a magnetic armature of material having a high hysteretic constant which comprises, operating the motor at an abnormally high magnetomotive force whenever the acceleration of said motor is above a given value, and reducing the magnetomotive force of the motor whenever the acceleration of said motor is less than said value, thereby to reduce the normal magnetizing current requiredby the motor.

2. The method of operating a hysteresis synchronous motor including a magnetic armature of material having a high hysteretic constant which comprises, operating the motor at an abnormally high'voltage whenever the acceleration of said motor is above a given value, and reducing the voltage of the motor whenever the acceleration of said motor is less than said value, thereby to reduce the normal magnetizing current required by the motor.

3. The method of operating a hysteresis synchronous motor including a magnetic armature of material having a high hysteretic constant which comprises, operating the motor at an abnormally high magnetomotive force whenever the acceleration of said motor is substantially above zero, and reducing the magnetomotive force of the motor whenever the acceleration of said motor falls substantially to zero, thereby to reduce the normal magnetizing current required by the motor.

4. The method of operating a hysteresis synchronous motor including running and starting windings and a magnetic armature of material having a high hysteretic constant which comprises, energizing both of said windings whenever the acceleration of said motor is above a given value, and energizing only said running winding whenever the acceleration of said motor is less than said value, thereby to reduce the normal magnetizing current required by the motor.

5. The method of operating a hysteresis synchronous motor including a plurality of phase windings and a magnetic armature o! a material having a high hysteretic constant which comprises, operating one phase winding of the motor momentarily at an abnormally high magnetomotive force to magnetize said armature, and thereafter reducing the magnetomotive force of thereby to reduce the normal magnetizing current required by the motor.

6. The method of operating a hysteresis synchronous motor including a plurality of phase windings and a magnetic armature of a material having a high hysteretic constant which comprises, operating one phase winding of the motor momentarily at an abnormally high voltage to magnetize said armature, and thereafter reducing the voltage or said one phase winding to its normal value, thereby to reduce the normal magnetizing current required by the motor.

7. The method of operating a hysteresis synchronous motor including a plurality of phase windings and a magnetic armature of a material having a high hysteretic constant which comprises, operating one phase winding of the motor at an abnormally high magnetomotive force whenever the acceleration of said motor is above a given value, and reducing the magnetomotive force of said one phase winding to .its normal value whenever the acceleration of said motor is less than said given value, thereby to reduce the normal magnetizing current required by the motor.

8. The method 01' operating a hysteresis sy'nchronous motor including a magnetic armature of material having a high hysteretic constant which comprises, starting the motor at a subnormal magnetomotive force, operating the motor at an abnormally high magnetomotive force whenever the acceleration of said motor is above a given value, and reducing the magnetomotive force of the motor whenever the acceleration of said motor is less than said value, thereby to reduce the normal magnetizing current required by the motor.

9. The method of operating a hysteresis synchronous motor including a magnetic armature of material having a high hysteretio constant which comprises, starting the motor at a subnormal voltage, operating the motor at an abnormally high voltage whenever the acceleration of said motor is above a'given value, and reducing the voltage of the motor whenever the acceleration of said motor is less than said value, thereby to reduce the normal magnetizing current ired by the motor.

10. The method of operating a hysteresis synchronous motor including a magnetic armature of material having a high hysteretic constant which comprises, operating the motor at an abnormallyhigh magnetomotive force whenever the acceleration of said motor is above a given value, and reducing the magnetomotive force or the motor to its normal value whenever the acceleration or said motor is less than said value, thereby to reduce the normal magnetizing current required by the motor.

11. An electric control system for a hysteresis synchronous motor including a magnetic armature of material having a high hysteretic constant comprising, an acceleration responsive device adapted to be driven by the motor, circuit-controlling means disposed to be actuated by said device, and an energizing circuit for the motor including said circuit-controlling means for developing in said motor an abnormally high mag netomotive force.

12. An electric control system for a hysteresis synchronous motor including a magnetic arma-- trolling means disposed to be actuated by said device whenever the acceleration of the motor is above a given value, and an energizing circuit for the motor including said circuit-controlling means for developing in said motor an abnormally high magnetomotive force.

13. An electric control system for a hysteresis synchronous motor including a magnetic armature of material having a high hysteretic constant comprising, an acceleration responsive device adapted to be driven by the motor, circuit-controlling means disposed to be actuated by said device whenever the acceleration of the motor is substantially above zero, and an energizing circuit or the motor including said circuit-controlling means for developing in said motor an abnormally high magnetomotive force.

14. An electric control system for a hysteresis synchronous'motor including running and starting windings and a magnetic armature o1 material having a high hysteretic constant comprising, an acceleration-responsive device adapted to be driven by the motor, circuit-controlling means disposed to be actuated by said device, and'an energizing circuit for the motor windings, the circuit of said starting winding including said circuit-controlling means for developing in said motor an abnormally high magnetomotive force.

15. An electric control system for a hysteresis synchronous motor including a magnetic armature of material having a high hysteretic constant comprising, a driven member adapted to be rotated by said motor, an inertia member having a lost-motion driving connection with said driven member, said driving connection having a resilient link, circuit-controlling means disposed to be actuated by said inertia member, and an energizing circuit for the motor including said circuitcontrolling means for developing in said motor anabnormally high magnetomotive force.

16. An electric control system for a hysteresis synchronous motor including a magnetic armature of material having a high hysteretic constant comprising, a threaded shaft adapted to be rotated by said motor, a flywheel threaded on said shaft, a tortion spring interconnecting said shaft and said flywheel for driving the latter, circuitcontrolling means disposed to be actuated by axial movement of said flywheel along said shaft,

and an energizing circuit for the motor including said circuit-controlling means for developing in said motor an abnormally high magnetomotive force.

17. An electric control system for a hysteresis synchronous motor including a multi-section winding and a magnetic armature of material having a high hysteretic constant comprising, an acceleration responsive device adapted to be driven by the motor, an energizing circuit for the motor winding, and circuit-controlling means disposed to be actuated by said device and connected to modify the connections of said winding sections for developing'in said motor an abnormally high magnetomotive force.

18. An electrical control system for a hysteresis synchronous motor including a multi-secticn winding and a magnetic armature oi material having a high hysteretic constant comprising, an acceleration-responsive device adapted to be driven by the motor, an energizing circuit for the motor winding, and circuit-controlling means 70 2'328743 12 disposed to be actuated by said device and connected to change the connections of said winding sections from series to parallel for developing in said motor an abnormally high magnetomotive force.

19. An electric control system for a hysteresis synchronous motor including a multi-section winding and a magnetic armature of material v g a i hysteretic constant comprising, an acceleration-responsive device adapted to be driven by the motor, an energizing circuit for the motor winding, and circuit-controlling means disposed to be actuated by said device and connected to decrease the number of winding sections connected to said energizing circuit for developing in said motor an abnormally high magnetomotive force.

20. Anelectric control system for a hysteresis synchronous motor including a magnetic armature of material having a high hysteretic constant comprising, an acceleration-responsive device adapted to be driven by the motor, an energizing circuit for the motor, impedance means normally in circuit with the motor, and circuitcontrolling means disposed to be actuated by said device for reducing the value of said impedance means effectively in circuit with the motor for developing in said motor an abnormally high magnetomotive force.

21. An electric control system for a hysteresis synchronous motor including a magnetic armature of material having a high hysteretic constant comprising, circuit-controlling means, an energizing circuit for the motor including said circuit-controlling means, and an acceleration-responsive device adapted to be driven by the motor and effective to actuate said circuit-controlling means to a first position for developing in said motor a subnormal starting magnetomotive force and to a second position for developing in said motor an abnormally high magnetomotive force.

22. An electric control system for a hysteresis synchronous motor including a magnetic armature of material having a high hysteretic constant comprising, circuit-controlling means, and an energizing circuit for the motor including said circuit-controlling means, an acceleration-responsive device adapted to be driven by the motor and effective during substantially zero acceleration of the motor to actuate said circuit-controlling means to a first position for developing in said motor a substantially normal magnetomotive force and eilective in response to acceleration of the motor substantially above zero to actuate said circuit-controlling means initially to a second position for developing in said motor a subnormal starting magnetomotive force and subsequently to a third position for developing in said motor an abnormally high magnetomotive force.

HERBERT C. ROTERS.

REFERENCES CITED The following references are of record in the file of this. patent:

UNITED STATES PATENTS Number Name Date 762,738 Myers June 14, 1904 Roters Sept. 7, 1943 

